Zakra scroll to top JS function

function scrollToTop() {
			var scrollToTopButton = document.getElementById( 'tg-scroll-to-top' );

			/* Only proceed when the button is present. */
			if ( scrollToTopButton ) {

				/* On scroll and show and hide button. */
				window.addEventListener(
					'scroll',
					function () {
						if ( 500 < window.scrollY ) {
							scrollToTopButton.classList.add( 'tg-scroll-to-top--show' );
						} else if ( 500 > window.scrollY ) {
							scrollToTopButton.classList.remove(
								'tg-scroll-to-top--show'
							);
						}
					}
				);

				/* Scroll to top when clicked on button. */
				scrollToTopButton.addEventListener(
					'click',
					function ( e ) {
						e.preventDefault();

						/* Only scroll to top if we are not in top */
						if ( 0 !== window.scrollY ) {
							window.scrollTo(
								{
									top     : 0,
									behavior: 'smooth'
								}
							);
						}
					}
				);
			}
		}